Expand the interface to WebURLLoaderTestDelegate.

Source/platform/blink_platform.gypi

 {
   'includes': [
     'platform_generated.gypi',
   ],
   'variables': {
     'platform_files': [
       'AsyncFileSystemCallbacks.h',
       'CalculationValue.h',
       'CheckedInt.h',
       'Clock.cpp',
@@ skipping 323 matching lines @@
       'exported/WebSpeechSynthesizerClientImpl.cpp',
       'exported/WebSpeechSynthesizerClientImpl.h',
       'exported/WebStorageQuotaCallbacks.cpp',
       'exported/WebThreadSafeData.cpp',
       'exported/WebThreadedDataReceiver.cpp',
       'exported/WebTraceLocation.cpp',
       'exported/WebTransformKeyframe.cpp',
       'exported/WebURL.cpp',
       'exported/WebURLError.cpp',
       'exported/WebURLLoaderClient.cpp',
+      'exported/WebURLLoaderTestDelegate.cpp',
       'exported/WebURLLoadTiming.cpp',
       'exported/WebURLRequest.cpp',
       'exported/WebURLRequestPrivate.h',
       'exported/WebURLResponse.cpp',
       'exported/WebURLResponsePrivate.h',
       'exported/WrappedResourceRequest.h',
       'exported/WrappedResourceResponse.h',
       'exported/linux/WebFontInfo.cpp',
       'exported/linux/WebFontRenderStyle.cpp',
       'fonts/AlternateFontFamily.h',
@@ skipping 700 matching lines @@
       ['os_posix==1 and OS!="mac"',
         {
           'platform_test_files': [
             'text/LocaleICUTest.cpp',
           ],
         }
       ],
     ],
   },
 }